This invention relates generally to electronic weighing and counting scales, and more specifically relates to a load cell especially useful in connection with such apparatus. While the load cell of the present invention is thus applicable to numerous types of weighing and/or counting scales and the like, it will--for purposes of concrete illustration--be described in connection with its use with an electronic scale particularly adapted to a counting function.
Thus it may be noted that in numerous industrial and commercial applications, a requirement exists for effecting a rapid and accurate determination of the number of unit pieces or articles present in a relatively large group of such individual units. For example, a manufacturer or shipper of small electronic components, or of relatively small hardware pieces such as washers or the like, may in the course of operations, require an accurate count of the number of individual units present in a large group of such like pieces.
In the past, various mechanically-actuated counting balances have been known for application to the aforementioned purposes. Mechanical devices of this type commonly, for example, utilize a pair of weighing platforms or cradles. A single article may be emplaced on one of the said platforms, with the plurality of the identical articles being positioned on the alternate platform. By such an arrangement, it is possible (after calibration) to determine the number of articles on the alternate of the mentioned platforms--i.e. in that the balance point is a function of the number of grouped units.
In general, such mechanically-actuated devices as above described, have proved to be relatively undesirable in continuous operation.
More recently, counting scales have been disclosed based upon modern electronic technology, with a load cell providing the desired inputs to the electronic circuitry. Thus, for example, in U.S. Pat. No. 4,043,412, a counting scale is disclosed which utilizes a single such load cell--which determines the weights of both a standardization sample and of the unknown quantity of articles in a group which is thereafter presented to the device.
While electronic counting scales, including devices such as disclosed in the aforementioned U.S. Pat. No. 4,043,412, have indeed been found effective in achieving their objectives, the versatility and dependability of such apparatus have been less than desired in a number of respects. In many such prior art devices for example, relatively conventional load cell structures are utilized, commonly based upon parallelogram flexure structures. Most of these prior art flexure structures include strain gauges at all flexing corners, thereby rendering it extremely difficult to compensate for gauge positioning errors; the said prior art structures are, further, subject to generation of second-order errors upon offset loading of the weight-receiving platform.
Further, the prior art electronic counting scales such as have been previously discussed, have been poorly adapted to use with a wide range of weight loads, i.e. generally, a given such device is adapted for use in counting groups of articles within a fairly narrowly-prescribed total weight range.
Furthermore, from a purely electronic viewpoint, numerous of these prior art electronic counting scales have been relatively lacking in long-term stability, and in features assuring accuracy and stability in count--as the number of objects successively added in the scale for counting is accumulated.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide a load cell design, utilizable in electronic weighing and/or counting scales or the like which load cell is based upon a parallelogram flexure of such design as to be uniquely free of second-order errors generated from offset loading of the force-receiving platform; which load cell structure is further, adapted for trimming to compensate for small symmetry errors present in the load cell as originally fabricated and assembled.